This specification defines a profile of the XMPP stream initiation extension for transferring files between two entities. The protocol provides a modular framework that enables the exchange of information about the file to be transferred as well as the negotiation of parameters such as the transport to be used.

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Warranty## NOTE WELL: This Specification is provided on an ”AS IS” BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, express or implied, including, without limitation, any warranties or conditions of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A PARTICULAR PURPOSE. ##

LiabilityIn no event and under no legal theory, whether in tort (including negligence), contract, or otherwise, unless required by applicable law (such as deliberate and grossly negligent acts) or agreed to in writing, shall the XMPP Standards Foundation or any author of this Specification be liable for damages, including any direct, indirect, special, incidental, or consequential damages of any character arising from, out of, or in connection with the Specification or the implementation, deployment, or other use of the Specification (including but not limited to damages for loss of goodwill, work stoppage, computer failure or malfunction, or any and all other commercial damages or losses), even if the XMPP Standards Foundation or such author has been advised of the possibility of such damages.

ConformanceThis XMPP Extension Protocol has been contributed in full conformance with the XSF’s Intellectual Property Rights Policy (a copy of which can be found at <http://xmpp.org/extensions/ipr-policy. shtml> or obtained by writing to XMPP Standards Foundation, 1899 Wynkoop Street, Suite 600, Denver, CO 80202 USA).

1 IntroductionThe traditional mechanism for transferring files in the Jabber community is the Out-of-Band Data 1 protocol. That protocol has several drawbacks: 1. It is not reliable. 2. It does not work when one of the parties is behind a firewall. 3. It provides limited metadata about files to be exchanged. The current document defines a profile of Stream Initiation 2 that solves the problems with out-of-band data, thus providing a robust, reliable mechanism for file transfers over the Jabber network. Implementors are referred to XEP-0095 regarding the underlying concepts of stream initiation.

2 Requirements? Enable seamless file transfer, including fall-back mechanisms as appropriate. ? Ensure that the profile will work even when one or both parties are behind a firewall. ? Define a full-featured set of metadata for file transfers, including the following: – – – – – description size name date hash

? Optionally support ranged transfers.

3 ProtocolThe file transfer profile is in the path” namespace. The profile is fairly simple: it consists of the root element with the possibility of one child describing the optional ranged transfers. The root element is <file> and has four attributes. The attributes are used only during the offer stage of stream initiation: ? size - The size, in bytes, of the data to be sent.1 2

XEP-0066: Out of Band Data <http://xmpp.org/extensions/xep-0066.html>. XEP-0095: Stream Initiation <http://xmpp.org/extensions/xep-0095.html>.

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4 EXAMPLES ? name - The name of the file that the Sender wishes to send. ? date - The last modification time of the file. This is specified using the DateTime profile as described in XMPP Date and Time Profiles 3 . ? hash - The MD5 sum of the file contents. The size and name attributes MUST be present in the profile. The other attributes MAY be present. There are two possible child elements of the root: <desc> and <range>. Both are OPTIONAL. <desc> is used to provide a sender-generated description of the file so the receiver can better understand what is being sent. It MUST NOT be sent in the result. When <range> is sent in the offer, it should have no attributes. This signifies that the sender can do ranged transfers. When a Stream Initiation result is sent with the <range> element, it uses these attributes: ? offset - Specifies the position, in bytes, to start transferring the file data from. This defaults to zero (0) if not specified. ? length - Specifies the number of bytes to retrieve starting at offset. This defaults to the length of the file from offset to the end. Both attributes are OPTIONAL on the <range> element. Sending no attributes is synonymous with not sending the <range> element. When no <range> element is sent in the Stream Initiation result, the Sender MUST send the complete file starting at offset 0. More generally, data is sent over the stream byte for byte starting at the offset position for the length specified.

3.1 Mandatory-to-Implement TechnologiesIn order to enable seamless file transfer and appropriate fall-back mechanisms, implementations of this profile MUST support both SOCKS5 Bytestreams 4 and In-Band Bytestreams 5 , to be preferred in that order. The associated namespaces are to be included as option values for the ”stream-method” variable as shown in the examples below. Additionally, implementations MAY support other mechanisms.

6.2 URI Query TypesAs authorized by XMPP URI Query Components 8 , the XMPP Registrar maintains a registry of queries and key-value pairs for use in XMPP URIs (see <http://xmpp.org/registrar/ querytypes.html>). As described below, the registered querytypes for file transfer actions are ”sendfile” and ”recvfile”. Note well that ”sendfile” means a second entity will send a file to the XMPP entity that controls the IRI/URI and that ”recvfile” means a second entity will receive a file from the XMPP entity that controls the IRI/URI.

6.2.1 sendfile To enable a second entity to send a file, the IRI/URI is of the following form: Listing 5: Sending a File: IRI/URIxmpp:romeo@montague . net / orchard ? sendfile6

The Internet Assigned Numbers Authority (IANA) is the central coordinator for the assignment of unique parameter values for Internet protocols, such as port numbers and URI schemes. For further information, see <http://www.iana.org/>. 7 The XMPP Registrar maintains a list of reserved protocol namespaces as well as registries of parameters used in the context of XMPP extension protocols approved by the XMPP Standards Foundation. For further information, see <http://xmpp.org/registrar/>. 8 XEP-0147: XMPP URI Query Components <http://xmpp.org/extensions/xep-0147.html>.